What are well-known entities functions?

"ISO 80000-2 Quantities and Units - Mathematics" provides a list of well-known functions. Here are some examples:

Integer Function - int(x) is defined as the integer part of a real number. For example:

<math><mi>int</mi><mo>⁡</mo><mn>3.14159</mn>
  <mo>=</mo><mn>3</mn></math>
    $\mathrm{int}3.14159=3$

Fraction Function - frac(x) is defined as the fraction part of a real number. For example:

<math><mi>frac</mi><mo>⁡</mo><mn>3.14159</mn>
  <mo>=</mo><mn>0.14159</mn></math>
    $\mathrm{frac}3.14159=0.14159$

Absolute Function - abs(x) is defined as the absolute value of a real number. For example:

<math><mi>abc</mi><mo>⁡</mo>
  <mo>(</mo><mrow><mo>&#x2212;</mo><mn>1.618</mn></mrow><mo>)</mo>
  <mo>=</mo><mn>1.618</mn></math>
    $\mathrm{abc}\left(-1.618\right)=1.618$

Minimum Function - min(...) is defined as the minimum value of all given arguments. For example:

<math><mi>min</mi><mo>&#x2061;</mo>
  <mo>(</mo><mn>3</mn><mo>,</mo><mn>1</mn><mo>)</mo>
  <mo>=</mo><mn>1</mn></math>
    $\min (3,1)=1$

Maximum Function - max(...) is defined as the maximum value of all given arguments.

Exponential Function - exp(x) is defined as the exponential value of x to the base of e. For example:

<math><mi>exp</mi><mo>&#x2061;</mo><mn>2</mn>
 <mo>=</mo><msup><mi mathvariant="normal">e</mi><mn>2</mn></msup></math>
    $\exp 2={\mathrm{e}}^2$

Logarithm Function - log_a(x) is defined as the logarithm value of x to the base of a. For example:

<math><msub><mi>log</mi><mn>2</mn></msub><mo>⁡</mo><mn>8</mn>
  <mo>=</mo><mn>3</mn></math>
    ${\log }_{2}8=3$

Natural Logarithm Function - ln(x) is defined as the logarithm value of x to the base of e. For example:

<math><mi>ln</mi><mo>⁡</mo><mn>8</mn><mo>=</mo>
  <msub><mi>log</mi><mn>e</mn></msub><mo>⁡</mo><mn>8</mn></math>
    $\ln 8={\log }_{\mathrm{e}}8$

Sine Function - sin(x) is defined as the sine value of x. For example:

<math><mi>sin</mi><mo>⁡</mo>
  <mi mathvariant="normal">π</mi><mo>=</mo><mn>0</mn></math>
    $\sin \mathrm{\pi }=0$

Other Trigonometric Function - cos(x), tan(x), cot(x), ... are defined as cosin, tangent, cotangent, ... functions.

⇒ List of Well-Known Operators

⇐ List of Well-Known Constants

⇑ ISO 80000-2 Quantities and Units - Mathematics

⇑⇑ MathML (Mathematical Markup Language)